Platelike projecting component portion of a gas turbine

ABSTRACT

A platelike projecting component portion ( 1 ) of a gas turbine or the like, with a surface ( 2 ) upon which hot gas acts and with cooling bores ( 12 ) through which a cooling medium is capable of flowing. Effective cooling is achieved in that at least one plenum ( 10; 30; 50 ) assigned solely to the component portion ( 1 ) is provided, which is arranged so as to be directly adjacent to the surface ( 2 ) upon which hot gas acts and through which the cooling medium is capable of flowing convectively, and in that, to form a cooling film, the cooling bores are designed as blow-out orifices ( 12; 52 ) which emanate from the plenum ( 10; 30, 50 ) and which issue on the surface ( 2 ) upon which hot gas acts.

[0001] The invention relates to a platelike projecting component portionof a gas turbine or the like according to the preamble of claim 1.

[0002] Component portions of this kind are often to be encounteredwhere, on grounds of construction, overhanging regions are to beprovided on main components, such as, for example, on blades andfastening elements, or sealing elements have to be mounted, even betweentwo adjacent components. Overhanging component portions of this kindpresent problems especially in regions which are subjected to highthermal load and in which hot gas acts upon the surface. It is oftenindispensable to provide cooling there.

[0003] EP 0 911 486 A2, from which the invention proceeds, discloses acooled blade of a gas turbine, in which are formed overhanging regionsin the form of platelike projecting component portions which are mountedin front of and behind the blade root in the axial direction, in orderto ensure in the hub region an overlap with the adjacent blade rootregions of rotor blades. For cooling these platelike projectingcomponent portions, cooling bores are provided, through which coolingair flows purely convectively. The cooling bores run, for example, inthe front overhanging component portion in the circumferential directionand are fed from the main cooling-air supply. Due to the high thermalload in this region, turbulence generators are additionally present inthe cooling bores in order to improve the heat transmission.

[0004] The rear overhanging component portion has a multiplicity ofaxially running cooling bores which are likewise fed from the maincooling-air supply. The cooling bores issue axially at the end of thecomponent portion, so that the cooling medium, after flowing through thecooling ducts, emerges into the hot-gas stream.

[0005] Both component portions have in common the fact that the surfaceupon which the hot gas acts is cooled purely convectively. Onedisadvantage of this is that a very large amount of cooling air has tobe expended in order to achieve the necessary cooling effect. Thisresults in an impairment of overall efficiency and makes it necessary toemploy costly materials resistant to high temperature.

[0006] The invention attempts to avoid the disadvantages described. Theobject on which it is based is to specify a platelike projectingcomponent portion of a gas turbine or the like of the type initiallymentioned which allows a more effective cooling of the surface uponwhich hot gas acts and therefore has an increased useful life, at thesame time with a reduced cooling-air requirement.

[0007] This is achieved, according to invention, in that, in a platelikeprojecting component portion according to the preamble of claim 1, aplenum is provided, which is assigned solely to the component portion,so that optimum cooling of the surface upon which hot gas acts becomespossible. The plenum is arranged so as to be directly adjacent to thesurface to be cooled and has the cooling medium flowing through itconvectively. Furthermore, the cooling bores are designed as blow-outorifices which emanate from the plenum and which issue on the surfaceupon which hot gas acts. It is thus possible to implement extremelyeffective film cooling on the surface upon which hot gas acts, while thecoolant consumption can be kept extremely low. The reason is that thecooling air first flows convectively through the region to be cooled, inorder thereafter, by being blown out, to form a highly effective coolingfilm.

[0008] Although, in principle, there is broad freedom of design asregards the configuration of the plenum, it has proved advantageous if asingle continuous plenum is provided, which passes essentiallycompletely through the component portion. In this way, the surface uponwhich hot gas acts is cooled uniformly and without local interruptioncaused, for example, by intermediate walls, with the result that acooling effect of hitherto unequalled effectiveness can be implemented.

[0009] A series of preferred design variants is aimed at the simple andcost-effective implementation of this cooling concept. The choice of theprocess for the optimum shaping of the plenum depends mainly on themethod of producing the actual component on which the platelikeprojecting portion is to be provided. Other important factors are thegeometry to be implemented and the manufacturing prerequisites.

[0010] As regards the turbine blade overhangs which are often to beencountered, it is appropriate to shape the plenum conjointly directlyduring shaping by the casting method. This is possible, as a rule,without much additional outlay, after removal from the casting mold theplenum being formed directly and without the need for subsequentmachining.

[0011] As a rule, a multipart core is used, in order to implement thedesired geometry of the plenum. If appropriate, lateral perforations forpositioning the core may be necessary, which can be closed subsequently,that is to say after the shaping process.

[0012] Alternatively to this, it is also possible to form the plenum bymeans of a cavity in the component portion, which cavity is open, forexample, opposite the surface to be cooled and can therefore be closedby means of a cover subsequently to be mounted. This avoids the need forproviding a core to form the plenum. The advantage of this variant isthe possibility of designing the geometry of the plenum to a largeextent freely.

[0013] The cover can be mounted by means of cost-effective connectionmethods, such as, for example, soldering or welding.

[0014] Finally, it is also possible to produce both the plenum and theblow-out orifices by means of the EDM method. With the aid of thismethod, in particular, the shape, size and arrangement of the blow-outorifices can be selected freely and implemented with the highestpossible precision. Also, the plenum as such can be implemented exactlyby means of this method. Lateral outflow orifices, such as are necessaryfor producing the plenum, may remain completely or partially open asadditional blow-out orifices, depending on the interpretation of thecooling concept. Otherwise, they are closed after the shaping operation.The plenum is preferably connected via feed ducts to a main plenum whichsupplies the blade with cooling air. No direct connection to thecooling-medium supply is therefore necessary, with the result that theoutlay in terms of construction can be reduced.

[0015] Although the above-described cooling concept can be implementedfor use in intrinsically any desired components subjected to highthermal loads, it is employed preferably on overhangs of turbine blades.There, on the one hand, the thermal loads are particularly high and, onthe other hand, a coolant supply is usually provided, in any case, inthe immediate vicinity of the overhang, with the result that the coolingconcept according to the invention can be implemented in a particularlysimple way.

[0016] Exemplary embodiments of the invention are illustrateddiagrammatically. shows a perspective view from above of an overhang ona turbine blade; shows a view from below of the overhang according toFIG. 1; shows a view from below of an overhang on a turbine bladeaccording to a first design variant; shows a core for producing aplenum; shows a view from below of an overhang on a turbine bladeaccording to a second design variant.

[0017] Only the elements essential for understanding the invention areshown and described.

[0018] The concept of the invention is explained with reference to aplatelike projecting component portion in the form of an overhang 1which is formed as an integral part of a platform 3 having a turbineblade 4. In this case, a surface 2 is subjected to high thermal load, tobe precise by a hot-gas jet which is not illustrated here. The designvariants described in more detail below are to this extent configuredidentically.

[0019] In the exemplary embodiment illustrated in FIG. 1 and FIG. 2,there are on the overhang 1 four plenums 10 which are arrangedessentially parallel to and at a distance from one another and whichpass continuously through the overhang 1. They run so as to be directlyadjacent to the surface 2 and cool the latter in this region by means ofa cooling medium, not illustrated in any more detail, which is conductedthrough convectively. There are also blow-out orifices 12, specificallypreferably arranged in rows and so as to be assigned to the plenums 10.They emanate from the plenums 10 and issue on the surface 2. In thisway, cooling medium is blown out of the plenums 10 through the blow-outorifices 12, in such a way that a coherent cooling film is formed. Thesurface 2 is thus cooled optimally.

[0020] As may be gathered, in particular, from FIG. 2, the plenums 10may be formed by EDM tools 19 which drill passage orifices into theoverhang 1. A connection is thus made with a main plenum 5 below theplatform 3, with the result that the plenums 10 are fed with cooling airfrom this region.

[0021] Depending on the requirement, the plenums 10 may issue, open,laterally on the overhang 1, as illustrated in FIG. 1. In this case,cooling air is additionally blown out of the overhang 1 laterally. It isequally possible, however, to close the plenums 10 partially orcompletely in this region.

[0022] The cross section of the individual plenums 10 may vary, in orderto achieve a cooling effect coordinated with the local heat load. Thisalso applies with regard to their number and the distribution of theirarrangement along the overhang 1. The same applies accordingly to thecooling bores or blow-out orifices 12 which are responsible for formingthe cooling film.

[0023] The design variant illustrated in FIG. 3 shows a plenum 30 whichpasses continuously, essentially completely, through the overhang 1 interms of its longitudinal and transverse extent. This allows a largelyideally equalized convective cooling of the surface 2 and, furthermore,affords the possibility of arranging the film-cooling air bores (notillustrated in any more detail here) so as to be distributedintrinsically in any desired way.

[0024] Again, the plenum 30 is supplied from the main plenum 5. For thispurpose, feed ducts 6 are provided, which make the connection betweenthe main plenum 5 and the plenum 30.

[0025] In this case, the plenum 30 and the feed ducts 6 are formeddirectly during the casting operation. For this purpose, a core 39,illustrated in FIG. 4, is used, which predetermines the shape of theplenum 30. Furthermore, two feed-duct portions 38 are provided, in orderto form the feed ducts 6. With the aid of this multipart core 38, 39,the plenum 30, including the feed ducts 6, can be formed in a simpleway.

[0026] The variant according to FIG. 5 shows a cavity 50 which is castin the overhang 1 and from which the cooling bores 52 emanate. Theactual plenum is formed when the cavity 50 is closed by means of a coverwhich is not illustrated here. The cover may consist of a simple platewhich is placed on to the overhang 1 and is soldered or welded there.Even complicated geometries can thus be implemented by means of acorresponding configuration of the cavity 50. Such geometries may be,for example, pins, ribs or turbulence generators (not illustrated) whichare arranged on the surface 2.

[0027] As already mentioned initially, the above-described concept isnot only restricted to use on overhangs of turbine blades, but, on thecontrary, use is possible wherever platelike projecting componentportions are exposed to high thermal loads and must therefore be cooledeffectively.

List of Reference Symbols

[0028]1 Overhang

[0029]2 Surface on the hot-gas side

[0030]3 Platform

[0031]4 Turbine blade

[0032]5 Main plenum

[0033]6 Feed duct

[0034]10 Plenum, EDM bore

[0035]12 Film-cooling bore, blow-out orifice

[0036]19 EDM tool

[0037]30 Plenum

[0038]38 Feed-duct portion

[0039]39 core

[0040]50 Cavity

[0041]52 Film-cooling bore, blow-out orifice

1. A platelike projecting component portion of a gas turbine or thelike, with a surface upon which hot gas acts and with cooling boresthrough which a cooling medium is capable of flowing, characterized inthat at least one plenum (10; 30; 50) assigned solely to the componentportion (1) is provided, which is arranged so as to be directly adjacentto the surface (2) upon which hot gas acts and through which the coolingmedium is capable of flowing convectively, and in that the cooling boresare designed as blow-out orifices (12; 52) which emanate from the plenum(10; 30, 50) and which issue on the surface (2) upon which hot gas acts,with the result that a cooling film can be generated.
 2. The componentportion as claimed in claim 1 , characterized in that the plenum (30,50) passes essentially completely through the component portion (1). 3.The component portion as claimed in claim 1 or 2 , characterized in thatthe plenum (30, 50) is formed by the casting method.
 4. The componentportion as claimed in claim 3 , characterized in that the plenum (30;50) is formed by means of a multipart core (38; 39).
 5. The componentportion as claimed in one of claims 1 to 4 , characterized in that theplenum (30; 50) is formed by a cavity (50) which is shaped into thecomponent portion (1) and which is closed by means of a cover.
 6. Thecomponent portion as claimed in claim 5 , characterized in that thecover is soldered or welded to the component portion (1).
 7. Thecomponent portion as claimed in claim 1 or 2 , characterized in that theplenum (10) and/or the blow-out orifices (12) is/are produced by the EDMmethod.
 8. The component portion as claimed in one of the precedingclaims, characterized in that the plenum (10; 30; 50) is connected to amain plenum (5) via feed ducts (6).
 9. The component portion as claimedin one of the preceding claims, in the form of an overhang (1) formed ona turbine blade (4).